The invention relates in general to force transducers such as gyroscopes and accelerometers and in particular to a closed loop control apparatus and method which provides a precise definition of the forces applied to maintain a force transducer system in a selected balanced condition.
Force transducers represent a class of force responsive elements in which the component elements of the transducer respond to externally applied forces by deviating or perturbating from a selected known and measured orientation or position. The component elements also respond to applied restoring forces to return the respective component elements to their selected known orientation or position. Typically, a force transducer further includes sensing devices for providing error singals having, for example, signal amplitudes proportional to the perturbation, from the selected orientation, of the transducer component elements.
Typical examples of force transducers are the gyroscope and the accelerometer. In the gyroscope, pointing errors, that is, a change from a selected orientation caused by an axial displacement of the gyroscope structure, cause an internal sensing element to provide an error signal. Gyroscopes are typically operated in either a closed loop or open loop mode; and in the closed loop mode, electrical signals responsive to the error signal are applied to torque motors or similar devices within the gyroscope assembly to return the gyroscope to its original known orientation relative to its case. This return to the original orientation corresponds, in turn, to a reduction of the error signal amplitude generated through the sensing element.
Accelerometers similarly provide an error signal, generated by a sensing element, when the assembly is subject to a "disturbing" acceleration (dv/dt) force. The accelerometer, like the gyroscope, operates in an open or a closed loop configuration; and accelerometer "movement" from a known orientation is compensated for by the application of a balancing restoring force generated in response to the error signal.
For both the gyroscope and the accelerometer, the magnitude and duration of the applied restoring forces provide a measurement of the forces (and hence of other physical parameters such as distance and velocity) to which the force transducer was subjected. As a result, it is important to be able to accurately measure the magnitude and duration of the externally generated restoring forces.
Previously, externally generated restoring forces were typically derived either in a continuous analog feedback loop or in a closed loop wherein the time axis was finely quantized to control the time duration during which forces were applied to return or hold the force transducer to or at the selected orientation. Both of these methods of generating the rebalance restoring force can be improved (in differing amounts) because the methods are unable to determine, with great precision, the time-duration/amplitude product of the forces applied to the force transducer over time periods of interest.
In those force transducers wherein the electrical restoring force signals are linearly related to the resulting restoring force applied to the transducer system, the ability of the external control system to determine and integrate the applied forces over time is acceptable using available time quantized systems. But, as the need for greater speed and stability grows, designers are choosing more efficient torque motors in which the restoring force applied to the transducer is proportional to the square of the applied electrical signal. None of the prior systems provide sufficient stability, precision, or reliability to enable the integral of the applied restoring forces to be accurately generated; and hence they are unable to determine with the generally required accuracy, the various measurement parameters used for proper operation of the apparatus incorporating the transducer.
A principal object of the invention is therefore a high reliablity, stable, and precisely controlled closed loop apparatus and method which enables the accurate determination of measurement parameters in force transducer systems employing square law electro-mechanical torquing elements. Other objects of the invention are an electrically simple, cost effective, reliable apparatus employing proven technologies to provide an accurate force transducer control apparatus and method. Yet another object of the invention is a control circuit and method for a gyroscope or an accelerometer which enable precision readout and high performance.